To measure the effect of sedimentation and bio-fouling on theglass surface of optical modules deployed in the deep sea.

•How do we measure?

We will periodically measure and record the singles at ½ speand doubles (in a 10ns window) PMT rates caused mainly byK40

decays and monitor the gain by recoding the singlephotoelectron pulse height.

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Autonomous Rate Measuring System

An Autonomous System

The PMT Rate Measuring System is an autonomous system, battery powered,designed to operate for more than 1 year with data recorded in memory andmonthly transfers acoustically to surface. Due to limited battery life of theacoustic modem, data transmitted has been designed to be only 40kB per month.

Battery life is also an issue for the rest of the electronics so low power electronicshave been designed and developed for this system.

The system will be in sleep mode most of the time. It will turn on only for 1 hourevery week to take the measurement, store the data and go to sleep mode again.It will also wake up to transmit the data upon acoustical request.

System total power consumption is:

On Mode: 40W

=> 40W x 52h = 2080Wh

Total power consumption = 3219Wh

Off Mode: 130mW => 130 x 8760h = 1139WhTotal power supplied = 8400Wh

Use of alkaline batteries

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System Description (Mechanical)

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APPARATUS LAYOUT (Side View)

Battery bank x 4

8 Optical Modules (4 pairs)

8ch HV Control

System Description (Electronics)

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OM1

OM2

OM3

OM4

OM5

OM6

OM7

OM8

4 ChannelDiscriminatorMAX964

4 Channel ADCAD7476

4 ChannelDiscriminatorMAX964

4 Channel ADCAD7476

FPGA

Spartan3E

SD

1GB

μController

PIC18F4550

SlowControls

Power Regulation&

Power DistributionSystem

Board to FPGA buses

8ch HV Monitor

Acoustic Modem

14bit bus

Assembled System

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Power Regulation and Power Distribution Unit

FPGA Board

Front End Electronics

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Discriminator

½ SPE

AMP

Peak and Hold

To Singles Rate

Counter

ADC

PMT Pulse

Inverted and

amplified PMT

Pulse

Discriminator

Pulse

CoincidenceLogic

To Doubles Rate

Counter

From Other

Discriminators

Conclusion

We have designed a low power autonomous system tomeasure the K40

rate to stay in the sea for more thanone year. It will be sensitive to reductions in the singlesand doubles rate at single photoelectron conditionsdue to sediment adhesion.

Data will be retrieved periodically acoustically.

Expected deployment end of this month. System iscurrently being tested at the Nestor Lab.